Novel Optical Chemosensors And Helical Self-Assembly Based On Naphthalene-and Perylene-bisimide Derivatives

Based on the molecular recognition principles, optial chemosensors and self-assembly have become two important branches of supramolecular chemistry. Optial chemosensors are highly valuable in a variety of fields such as environmental chemistry, analytic chemistry and bio-medicinal science because they can provide accurate, on-line, and low-cost detection of toxic heavy metal ions with high selectivity and sensitivity. Unfortunately, the main application problems with most biolocal fluorescent sensors are short emission wavelength strongly disturbed by the auto-and/or background-fluorescence and harmful to the living tissues and biomass. Since the remarkable near-infrared (NIR) emission can eliminate the influence of above-mentioned disadvantages, the exploiture of NIR biological dyes and NIR fluorescent chemosensors has been of great value for both in vitro and in vivo biological applications.Compared to the relatively well-developed coordination-based chemosensors, irreversible-chemical-reaction-based chemodosimeters have recently emerged as a research area of significant importance due to its highly analyte-specific property and providing signaling changes in both the absorption wavelength and color, which can be detected by the naked eye. Furthermore, supramolecular self-assembly is one of the key techniques for the "bottom-up" approach in nanotechnology, by which small molecules from well-defined larger nanostructures via multiple non-covalent intermolecular forces, including hydrogen-bonding,π-πstaking and so on. In particular, the precise control of chiral building blocks is essential to supramolecular helical performance.The aim of this thesis is to develop new fluorescent chemosensors and chemodosimeters based on novel naphthalene diimide (NDI) and perylene bisimides (PBI) dyes. Additionally, perylene-bisimide-based self-assemblies are also discussed.In Chapter 1, the major sensing principles of optical chemosensors are introduced, and the progress in NIR fluorescent chemosensors, chemodosimeters for Hg2+, and supramolecular helical self-assemblies is reviewed.In Chapter 2, eight highly colored and photoluminescent mono-or di-core-substituted naphthalene diimide (NDIs) have been rationally designed and synthesized from 2,6-dibromonaphthalene diimide (DBI) by means of a stepwise nucleophilic substitution of two bromine atoms by heterocyclic secondary amines, which have been characterized by a wide range of spectroscopic methods. Electronic absorption and fluorescence studies revealed that the amine substituents with different electron-donating abilities leads to the NDIs with tuneable absorption and emission properties, falling in the preferable region to NIR (λabsmax: 509～580 nm;λemmax:565～638 nm;ΦF:0.21～0.54; Stokes shift:36～77nm).In Chapter 3, two novel NIR fluorescent "turn-on" chemosensors (PND and PNT) for Zn2+ based on NDI fluorophore have been designed, synthesized and optimized as well. Our strategy was to choose NDI as a novel NIR fluorophore, and DPEA or TPEA as the receptor, respectively, so as to improve the selectivity to Zn2+. In the case of PND, The nearly 4-fold fluorescence enhancement and the negligible shift in absorption and emission spectra of PND with Zn2+ titration are dominated with a typical photoinduced electron-transfer (PET) process, resulting in the formation of a three-coordinate Zn2+-PND complex. In contrast, the distinct blueshift in both absorbance and fluorescence is indicative of a combination of PET and ICT processes, giving a more stable five-coordinate Zn2+-PNT complex. Due to the differential binding mode caused by the ligand effect, PND shows excellent selectivity to Zn2+ over other metal ions but lower sensitivity when compared with PNT. Also both PND and PNT were successfully used to image intracellular Zn2+ ions in the living KB cells, indicating high cell-permeability and low toxicity. To our best knowledge, this is the first report of NIR cation chemosensors based on NDI as fluorophore, which may be helpful to tailor NDI as reporter groups to be specific for the other NIR cation chemosensors.In Chapter 4, three novel NDI derivatives (PN1, PN2 and PN3) with different isothiocyanate substituents as dosimeter units via the specific Hg2+ -induced desulfurization have been synthesized for developing colorimetric chemodosimeters to Hg+. The distinct response is dependent on the electron-donating effect of isothiocyanate substituents, that is, the stronger in the electron-donating capability of isothiocyanate substituents, the faster in the Hg2+ -promoted cyclization. Both PN1 and PN3 with Hg2+ exhibit color changes from blue to wine-red (with blue shifts of 25 and 44nm in absorption, respectively), fully meeting "naked-eye" colorimetric changes with a detection limit of 5μM. In addition, PN3 also successfully developed as Hg2+ test kits with a discernible concentration of 10μM.Chapter 5 describes an unprecedented Hg(OAc)2-induced N-acetylation of 1,3-disubstituted thioureas, involving the intermediate of carbodiimide. Accroding to the mechanism of Hg(OAc)2-induced N-acetylation of 1,3-disubstituted thioureas, a novel chemosensor P3 based on perylenebisimide (PBI) as signaling moiety and thiourea as reactive moiety has been designed and synthesized as a turn-on fluorescent chemodosimeter towards highly sensitivity and selectivity for Hg2+ among common metal ions, in an acetate aqueous medium.Little attention has been paid to the O-H...O hydrogen bonding interactions in the PBI system although the conventional hydrogen bonding in carboxylic acids is particularly strong in solutions, on surface and in crystal with high sensitivity to various environmental factors. In Chapter 6, our motivation is focused on borrowing the help of O-H...O hydrogen bonding interactions to realize the control in chiral self-assembly. For this purpose, we construct the target chiral a-amino acid system based on PBI system with the following considerations:i) to obtain PBIs bearing the self-assembly unit of carboxylic groups, chiral a-amino acid is an obviously good choice to the building block with an easy imidation to incorporate carboxylic groups and retain the original chiral center of amino acid; ii) incorporating the substitute of 4-methylphenoxy to their bay-region at PBI to prevent the competitive H- or J-aggregation during the interaction process of hydrogen bonding; iii) attempting to realize helical arrangement via the chiral center control with two exact enantiomers of L- and D-phenylalanine. The combination of optical, 1H NMR and CD spectra allows the observation of chirality-controlled helical superstructure in a self-assembled perylene bisimide system via intermolecular hydrogen-bonding. Interestingly, the chiral carboxylic acid-functionalized PBI systems are found to be spontaneously self-assembled into supramolecular helices, which are strongly dependent upon several factors, such as solvent polarity, concentration and temperature. Moreover, the supramolecular helical chirality can be well controlled by the chiral amino acid residues in PBI system, that is, the assembled clockwise (Plus, P) or anticlockwise (Minus,M) helices can be induced by L-or D-isomers, respectively, which also further assemble into hollow nanospheres in the solid state (AFM study).